This invention relates to a thermostatic valve for controlling the temperature of the coolant of an internal-combustion engine, particularly of a motor vehicle engine. Such valves typically control the coolant flow from the engine through a bypass and/or heat exchanger, and back to the engine. In a known construction, a valve body is provided which contains an expansion agent carries one or more valve disks and has a working piston which moves out of the valve body when it is heated to cause movement of the valve disks to open the valve. The valve body is typically spring-biased toward the closed position. The working piston interacts with a support body which can be adjusted by means of a regulating unit and which provides a reactive bearing surface for the piston. The valve characteristics can be adjusted by varying the distance between the bearing surface and the valve body.
In a thermostatic valve of the above mentioned type (i.e., a thermostatic valve having a valve body containing an expansion agent and a working piston which can be moved outwardly from the body--German Published Unexamined Patent Application No. DE-OS 32 26 104), this valve construction has proven itself many times in practice. By changing the distances between the control or bearing surface of the support body and the valve body, the valve characteristics can be changed so that control of the temperature of the internal-combustion engine, via the temperature of the coolant, is possible. This control can use the ambient or outside temperature or other parameters as control variables, such as the exhaust gas temperature, the speed and/or the torque of the engine, the vacuum in the suction or intake pipe, the pressure difference in a vacuum box, the oil temperature and other variables.
In a practical application using this type of thermostatic valve, operating conditions may arise in which the control is disrupted and unwanted or undesirable results are obtained. A wax or a wax mixture which is selected for a certain temperature range is conventionally used as the expansion agent. The regulating or adjusting unit preferably includes an electric motor drive. When the internal-combustion engine is switched off, the electric-motor drive is also switched off so that the regulation unit remains in its respective control position. As the temperature of the coolant decreases, the wax serving as the expansion agent solidifies so that the working piston of the thermostatic valve also remains in its respective position. When the internal-combustion engine is re-started under different operating conditions, which may be expected by the time the coolant temperature has gone down, the support body is adjusted by the regulating unit into a control position which corresponds to these operating conditions. When, during this adjustment, the control surface of the support body is moved closer to the valve body of the thermostatic valve, the valve body is shifted causing the thermostatic valve to open because the working piston cannot be pressed into the valve body due to the solidified wax. This result disturbs the intended control arrangement and can lead to undesirable operating conditions of the internal-combustion engine.
An object of this invention is to provide a thermostatic valve of the above-mentioned type in which no such disturbances in the control arrangement occur when the internal-combustion engine is started.
This development ensures that the working piston, after each switching-off of the internal-combustion engine and subsequent cooling of the coolant, is restored or placed back in the valve body so that, when the engine is started again, the support body can be adjusted by the regulating unit into the position that corresponds to the desired control condition, without causing the valve to open. When a restoring spring is used, the size of the spring and/or its arrangement in the valve are selected so as to ensure that other components of the thermostatic valve are not adversely affected (e.g., so that undue force is not exerted against the spring which biases the valve body toward the closed position.
In an especially advantageous embodiment of the invention, it is provided that the restoring path of the working piston (i.e., the distance or range of movement of the piston during restoration) is limited by a stop. To avoid interference with the control arrangement, it is sufficient to place the working piston back along a restoring path that corresponds to the maximum path or adjusting distance variation of the control surface of the support body. By limiting the path of the working piston, the effect of the restoring means is at the same time limited to this path. The result is, on the one hand, that the restoring means does not constantly affect the sealing element which separates the working piston from the area inside the valve body containing the expansion agent. In addition, when the working piston is in the restored position, the restoring means does not affect the closing spring, which is generally provided to hold the valve disks in the closed position, so that an unintended removal of load from the closing spring is avoided. In another embodiment of the invention, the restoring path of the restoring means is limited. This results in the same effect concerning the removal of load from the closing spring and from the sealing element.
In another advantageous embodiment of the invention, the electric circuit of the regulating unit provides a switch-off step or signal by means of which, when the internal-combustion engine is turned off, the regulating unit is adjusted into an end position which corresponds to the moved-in or restored position of the working piston.